Variable venturi



Oct. 13, 1959 L. F. STEWART VARIABLE [VENTURI Filed Nov. 7, 1957 METER/N6 FUEL sou/Pas INVENTOR.

' ATTORNQY.

YARIABLE Leonard F. Stewart, Flint, Mich., assignor to General Motors Corporation, ';Detroit, "Mich a corporation of Delaware Application November 7, 1951, Serial No. 695,012

7Claims. 01.261-59 I The presentinventionrelates to a fuel metering device fora fuel injection system andmore particularly such a device embodyingan improved type of flow measuring device.

(In fuel systems which utilize air flow venturis for the purpose of measuring the quantity of fuel to be .metered, ,it haslong beena problem in using a fixed sized tventuri to select the-proper size for all operating conditions. Such a choiceis infact impossible sincea venturi throat size which isadeguate-to-give a proper metering signal under low air flow conditions will seriously re strictthe quantitylof air flowlunder high speed operating conditions. On the other hand, venturithroats large enough ,to accommodate ,high volume air flow will not provide satisfactory metering signals under low air flow conditions.

Ithas been the practice to;use a venturi in which the throat size is compromised between that desirable for a strong-low air flow signal andthat capable of providing .sutficient air ,for high speed toperation, Another compromise solution hasgbeen to provide a pair-of paral- .lel.related :venturis with a small venturi being utilized under low airflow conditions and a .larger venturi being combined therewith .to provide the requisite airflow duringhigh speed operating conditions. i t

.It is thepurpose of the present invention to providea unique automatically adjustable ,venturi which is capable of providing a .strongmetering signal during lowair flow conditions as .wellas permitting suflicient air flow therethrough to meet .high speed operating requirements. It is also anobject of the present invention to provide an adjustable throat venturi whichis simple and inexpensive to manufacture and which is yet capable of responding accurately to the needs of the enginegwith which it is associated.

More specifically .it is an object of .the present inven- .tion to provide an adjustable .vfi ltur-i which is automatically controlled in response to the-air flow therethrough. The subject variable venturi is particularly well adapted for .use with a fuel injection systemof the type in which a quantity of fuel supplied to the engine is metered in accordance with ,the massor quantity of air flow through the induction passage as illustrated incopending application Serial No. 591,889 Dolza, filed June .18, 1956.

.Otherobjects and adyantagespf the present invention will beapparent from a. perusal .of the detailed descrippresent invention.

ted States Patent 23%,488 Patented Oct. .13, 1959 ice An air intake or inductioncasing 12 includes passage 14 in which a throttle valve :16 ismounted for controlling the quantity of combustible charge supplied to the associated engine. The induction passage 1.4 communicates with a plurality of individual cylinder inlet passages 18 each of which includes a fuel nozzle .20 disposed adjacent the respcctiveenginecylinder intake valves 22.

A fuel source is indicated generally at 24 and is adapted to supply fuel underpressure to a metering valve 26 through a conduit 28. Valve 26 in turn supplies a metered quantity of fuel through conduits 30 -to each of the fuel nozzles 20. As described in the aforenoted copending application, .anexcess quantity of .fuelis normally supplied to the metering valve 26 .with theexcess fuel being returned .to .the fuel source through a passage 32. The quantity of fuel bypassed by the metering valve 26, which therefore determines the quantity of fuel supplied to .the nozzles 20, .is determined by a metering diaphragm 34mounted in a casing 36.

An annular chamber 38 is formed -in the induction casing 12 and openly communicates at its radially inner end with induction passage .14. .In conjunction with means to subsequently be described, a vacuum force is created -in .chamber 38 which is proportional to the quantity of airflow through the induction passage .14. The vacuum force in chamber 38 is communicated through a passage 40 with the metering control diaphragm 34 in such a way that as-the vacuum force increases the diaphragm .is raised against the force .of spring-43 .to increase the quantity of fuel supplied by metering valve 26 to the nozzles 20. i

The venturi or air meter .10 also includes a servo controlled tapered plug .member indicated generally at 42 which is mounted -on and in axially spaced relation :to a flange. 44 formed .on .the induction-casing 12. Member 42 is supported on casing 12 .by means of a plurality of circumferentially spaced studs 46. Plug memberl42 and inductioncasing 12 cooperate to form an :annular radial air intake 48 through which :aircis drawn into the ,induction passage 14.

More specifically, the plug member 42 includes a dished .casing member 50 having a centrally apertured boss portion 52 depending therefrom. An upwardly dished 'cover member '54 is mounted on casing 50 through a plurality of-stud members 56. Casings 50 and 54 are adapted to peripherally clamp :a flexible diaphragm member 58 therebetween. Diaphragm 58 has a rod 60 centrally fixed thereto and which rod projects through the aperture or passage 62 in boss 52. In order to reinforce the diaphragm 58 in its connection to rod 60 a pair of reinforcing washers 64 are clamped on either side thereof and in turn connect with a collar 66 fixed to rod 60.

The other end of rod 60 centrally supports an inverted frusto-conicalmember '68. Member 68 is hollow being closed at one end and having its open end terminating adjacent casing 150. Casing 50 is formed to provide an annular opening 70 in the bottom surface thereof and which opening is concentrically related to conical member 68. Opening 70 is sufficiently large'to receive the open end of conical member 68 in relatively axially slidable relation. A spring member 72 is adapted to seat upon the casing 50 in generally concentric relation to the boss '52 and to bias against the closed end of the member 68 to urge the latter into induction casing 12 to restrict the quantity of air flow through passage 14.

Diaphragm 58 and cover 54 coact to define a chamber '74 to which the vacuum force in conduit 40 is admitted through a branch passage 76 and boss 78. Since the apertured passage 62 inboss '52 is of a greater diam eter thanrod '60, the chamber 80 defined-by casing 50 and diaphragm 58 is maintained at substantially atmospheric pressure, Thus it will be seen that the vacuum in induction casing chamber 38, which is suitably transmitted to the venturi meter chamber 74, tends to urge the diaphragm 58 and hence the conical.member 68 in an upwardly direction against the force of spring 72 as the air flow through the induction passage increases.

As the air flow through the induction passage 14 increases the increased vacuum force in conduit 40 will be simultaneously transmitted to diaphragms 34 and 54 increasing the quantity of fuel flow to nozzles 20 and at the same time reducing the restriction to air llow through air meter consonant with the increased fuel/air requirements of the engine. On the other hand, as the engine draws less air through induction passage 14 the vacuum force in chamber 38 will decrease permitting spring 72 to move the conical plug 68 more deeply into the induction passage maintaining the velocity of the air flow through the venturi at a sufficiently high value to maintain a relatively strong metering signal in chamber 38.

With a fixed size venturi it has been found that under low air flow conditions, as occurs during engine idling conditions, the venturi vacuum metering signal is so low as to be insuificient to accurately control the fuel metering valve. For this reason it has been necessary to provide means for reinforcing or supplementing the metering signal under these low air flow conditions. An expedient has been to admit a secondary force such as manifold vacuum or a vacuum force created by a secondary venturi action related to idle air flow the latter as shown in copending application Serial No. 608,797, Olson, filed September 10, 1956. The latter expedient while helpful is limited to idle or ofi-idle operation whereas the former expedient introduces a control force somewhat inimical to a true mass air flow system.

The present air metering device 10, on the other hand, by providing servo means for regulating the venturi throat size in accordance with induction air flow continuously maintains air velocity at a level to insure an adequate fuel metering signal under all air flow conditions.

I claim: V

1. A fuel injection system for an internal combustion engine of the type including an induction passage for delivering air to the cylinders of'the engine, a source of fuel under pressure, a fuel metering valve, a control member operatively connected to said metering valve, an air metering device associated with said induction passage for providing a control signal to the metering valve control member which is proportional to the mass of air flow through said induction passage, in which said air metering device comprises a venturi formed by said induction passage and a tapered plug projecting within said passage, and means for moving said tapered plug axially of the induction passage to change the cross sectional area of said venturi to control the strength of said metering valve control force.

2. A fuel injection system for an internal combustion engine of the type including an induction passage for delivering air to the cylinders of the engine, a source of fuel under pressure, a fuel metering valve, a control member operatively connected to said metering valve and an air metering device associated with said induction passage for providing a control signal to the metering valve control member which is proportional to the mass of air flow through said induction passage, in which said air metering device comprises a venturi formed by said induction passage and a tapered plug projecting within said passage, and means responsive to the quantity of induction passage air flow for moving said tapered plug axially of the induction passage to change the cross sectional area of said venturi to control the strength of said metering valve control force.

3. A fuel injection system for an internal combustion engine of the type including an induction passage for delivering air to the cylinders of the engine, as ource of fuel under pressure, a fuel metering valve, a control member operatively connected to said metering valve and an air metering device associated with said induction passage for providing a control signal to the metering valve control member which is proportional to the mass of air flow through said induction passage, in which said air metering device comprises a venturi formed by said induction passage and a tapered plug projecting within said passage, and means for moving said tapered plug axially of the induction passage to change the cross sectional area of said venturi, said plug moving means being actuatable in response to the metering control signal to increase the venturi cross sectional area as said signal increases.

4. A fuel injection system for an internal combustion engine including an air induction passage for delivering air to the cylinders of the engine, a tapered plug adjustably mounted in said passage to define a venturi therewith, first servo means for adjusting said plug to vary the velocity of air flow therethrough, a source of fuel under pressure, a valve for supplying metered quantities of fuel from said source to said cylinders, second servo means for controlling said valve, and common means responsive to the mass of air flow through said passage for controlling said servos.

5. An air metering device for an internal combustion engine comprising an air induction passage, throttle means for controlling the quantity of air flow through said induction passage, a casing member mounted on said induction passage wall in axially spaced relation thereto, a tapered plug member supported from said casing and projecting within said induction passage, said plug c0- acting with said induction passage to define an annular venturi, an annular chamber formed in said induction passage at the throat of said venturi and in open communication therewith, said annular chamber being so related to said venturi throat that a vacuum force is created therein which is proportional to the mass of air flow through said induction passage, means for moving said plug axially relatively to the induction passage to vary the cross sectional area of said venturi whereby said cross sectional area will be increased in proportion to the mass of air flow through said induction passage.

6. An air metering device for an internal combustion engine comprising an air induction passage, throttle means for controlling the quantity of air flow through said induction passage, a casing member mounted on said induction passage wall in axially spaced relation thereto, a tapered plug member supported from said casing and projecting within said induction passage, said plug coacting with said induction passage to define an annular venturi, an annular chamber formed in said induction passage at the throat of said venturi and in open communication therewith, said annular chamber being so related to said venturi throat that a vacuum force is created therein which is proportional to the mass of air'fiow through said induction passage, means for supplying metered quantities of fuel to the engine cylinders, means for moving said plug axially relatively to the induction passage to vary the cross sectional area of said venturi, said vacuum force being adapted to actuate said latter two means to increase the venturi cross sectional area and the fuel supplied to'the cylinders as air flow increases.

7. An air metering device for an internal combustion engine comprising an air induction passage, throttle means for controlling the quantity of air flow through said induction passage, a casing member mounted on said induction passage wall in axially spaced relation thereto, a tapered plug member supported from said casing and projecting within said induction passage, said plug coacting with said induction passage to define an annular venturi, an annular chamber formed in said induction passage at the throat of said venturi and in open communication therewith, said annular chamber being so related to said venturi throat that a vacuum force is cre- 6 ated therein Which is proportional to the mass of air flow tional area of the venturi with a force proportional to inthrough said induction passage, spring means for moving I duction passage air flow. said plug axially relative to the induction passage to decrease the cross sectional area of said venturi, a servo- References Cited in the file of this Pawnt motor operatively connected to said plug, and conduit 5 U T D STATES PATENTS means communicating said annular chamber and servo 2,788082 vanderpoel APR 9 1957 whereby said vacuum will tend to increase the cross sec- 

